1. Field of the Invention
The present invention relates to a developing apparatus used in an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer.
2. Related Background Art
In the image forming apparatus of an electrophotographic system, an electrostatic latent image formed on an image bearing member is developed by a developing apparatus and is visualized as a toner image. In an image forming apparatus for forming a color image by overlapping toner images of plural colors, an image forming apparatus using an intermediate transfer member as shown in FIG. 15 is proposed and practically used to form a color image having no color shift. In this image forming apparatus, the image can be formed by using the intermediate transfer member irrespective of sizes and thicknesses of a transfer member, etc. and media flexibility is also improved.
An image forming process in the image forming apparatus in FIG. 15 will be explained. The image forming apparatus is connected to a host device 112 such as a personal computer and a work station, and receives image data through a video interface by a print request from the host device 112. These image data are decomposed into four colors of yellow, magenta, cyan and black, and charge, exposure and development processes are sequentially performed in each color with respect to a photosensitive drum 110 so that toner images are formed. These toner images are overlapped and transferred to the intermediate transfer member (intermediate transfer drum) 105 of a drum shape. Thereafter, these toner images are transferred together to a recording material such as paper as a recording medium so that a full color image is formed on the recording material.
The photosensitive drum 110 as a first image bearing member is rotated at a predetermined circumferential speed in an arrow direction. A surface of this photosensitive drum 110 is uniformly charged by a charging roller 102 as a charging means. The charging roller 102 comes in press contact with the surface of the photosensitive drum 110 with predetermined pressing force, and charges the photosensitive drum 110 while the charging roller 102 is driven and rotated by the rotation of the photosensitive drum 110. Next, a scanning operation is performed by an exposure means 103 on/off-controlled in accordance with image data of a first color (e.g., yellow), and an electrostatic latent image of the first color is formed on the surface of the photosensitive drum 110. This electrostatic latent image of the first color is developed by a developing apparatus 104Y storing yellow toner among plural developing apparatuses 104 and is visualized as a yellow toner image. The developing apparatuses 104 (104Y to 104K) will be described later.
The toner image of the first color formed on the photosensitive drum 110 is transferred to a surface of the intermediate transfer drum 105 (primary transfer). The intermediate transfer drum 105 as a second image bearing member comes in press in contact with the photosensitive drum 110 with constant pressing force, and is rotated in an arrow direction in FIG. 15 at a circumferential speed approximately equal to that of the photosensitive drum 110. The toner untransferred but left on the surface of the photosensitive drum 110 in the primary transfer is scraped by a cleaning blade 106a of a cleaner 106 coming in press contact with the photosensitive drum 110 and is stored into a waste toner container 106b. 
The above processes are also repeated with respect to magenta, cyan and black. Every time a magenta toner image of a second color, a cyan toner image of a third color and a black toner image of a fourth color are obtained, the toner images are sequentially transferred onto the intermediate transfer drum 105. Thus, a full color image obtained by overlapping the toner images of the four colors is formed on the intermediate transfer drum 105.
The full color image on the intermediate transfer drum 105 is electrostatically transferred together to a recording material P fed from a paper cassette 108, etc. by a secondary transfer roller 109 (secondary transfer). Thereafter, the recording material P is sent to a fixing apparatus 107 and the four toner images are fixed. Thereafter, the recording material P is discharged from a discharging portion to the exterior of the apparatus so that a predetermined desirable print image is obtained.
The developing apparatuses 104 (104Y, 104M, 104C, 104K) in the above image forming apparatus are not particularly limited, but dry type one-component developing apparatuses are variously proposed as one of the developing apparatuses and are practically used. This is because the developing apparatus can be generally made compact and simplified in structure by a dry type one-component developing method. However, a problem exists in that it is difficult to form a thin layer of toner as a one-component developer on a developer bearing member in any of the developing apparatuses of the dry type one-component system.
However, developments with respect to thin layer forming method and apparatus of toner are indispensable since improvements of resolution and clearness of the image, etc. are required at present. Therefore, some measures with respect to this problem are proposed.
For example, as shown in Japanese Patent Application Laid-Open No. 54-43038 (1979), a developing blade (an elastic regulating member) made of rubber or a metal abuts on the developer bearing member and toner passes through an abutting portion between this developing blade and the developer bearing member and is regulated. Thus, a toner thin layer is formed on the developer bearing member and sufficient frictional charged charges (triboelectricity) are given to the toner by friction in the abutting portion. This dry type one-component developing apparatus and the thin layer forming method do not limit the toner (one-component toner) as a one-component developer at all.
In the case of magnetic toner, a developing apparatus as shown in FIG. 16 is proposed. In this developing apparatus 104, toner is supplied and borne onto a developing sleeve 121 (developer bearing member) by magnetic force of a magnet 113 of a roller shape arranged within the developing sleeve 121. The toner passes through an abutting portion between the developing sleeve 121 and a developing blade 122 and is regulated so that a toner thin layer is formed on the developing sleeve 121. In the case of nonmagnetic toner, it is necessary to separately arrange a toner supply member for supplying the toner onto the developing sleeve. This is because no nonmagnetic toner is supplied by magnetic force.
Therefore, a developing apparatus as shown in FIG. 17 is proposed as the developing apparatus using nonmagnetic toner. In this developing apparatus 104, a toner supply roller 123 is arranged in a position of a developing sleeve 121 on its upstream side from a developing blade 122 in a rotating direction of this developing sleeve 121 within a developing container 126 storing nonmagnetic toner T as a one-component developer. The toner supply roller 123 is constructed by using a foam body formed by polyurethane foam, sponge, etc., or a fur brush abutting on the developing sleeve 121. The toner T is supplied and borne onto the developing sleeve 121 by rotating this toner supply roller 123 in an arrow direction.
The toner borne onto the developing sleeve 121 is sent to an abutting portion of the developing sleeve 121 and the developing blade 122 as the developing sleeve 121 is rotated. The toner is regulated and formed as a thin layer in this abutting portion. Thereafter, the toner is carried to a developing portion opposed to the photosensitive drum 110 and is used to develop an electrostatic latent image on the photosensitive drum. The toner unconsumed in the development but left on the developing sleeve 121 is returned to the interior of the developing container 126 as the developing sleeve 121 is rotated. This toner is then scraped by the supply roller 123. Simultaneously, as mentioned above, new toner is supplied onto the developing sleeve 121 by the supply roller 123.
When the developing sleeve 121 is manufactured by a metallic material, it is not preferable to use a metallic thin plate as the developing blade 122 in view of wearing of the developing sleeve 121. It is necessary to use a rubber material such as urethane, silicon on an abutting face of the developing blade 122 on the developing sleeve 121 so as to obtain a preferable toner thin layer. When the developing sleeve 121 is manufactured by a rubber material such as urethane, silicon, each of a metallic thin plate and a rubber material such as urethane and silicon can be used in the developing blade 122.
Improvements of resolution and clearness of an image, etc. are similarly required in the toner of a one-component developer used in the above developing apparatus 104.
With respect to the improvement of a transfer property of the toner, it has been found that transfer efficiency can be greatly improved as an acting effect of a toner shape by forming the toner in a spherical shape in comparison with the toner of an undefined shape manufactured by a conventional grinding method. There are mainly the following two methods as a method for manufacturing the spherical toner.
(1) Plastic spherical processing of a surface of the conventional grinding toner is performed by thermal stress and mechanical stress. (2) The spherical toner is manufactured by a polymerizing method.
Further, in the above methods, attachment and dissociation of externally-added fine powder with respect to the toner are repeated by a shearing force applied to the externally-added fine powder within the developing container. Therefore, the number of contact times of the fine powder and the toner is increased so that frictional charged charges of the toner can be increased and a developing property of the toner can be improved.
For example, as shown in Japanese Patent Application Laid-Open No. 60-32060 (1985), a polishing agent component can be externally added to the toner with respect to phenomena of filming and toner melting attachment in which the toner left on the photosensitive drum is strongly fixed and deposited by a cleaning blade and a charging roller coming in press contact with the photosensitive drum at a predetermined pressure. It is possible to prevent the toner left on the photosensitive drum from being strongly fixed and deposited in advance by suitably polishing the surface of the photosensitive drum by the polishing agent component.
However, when a developing operation is performed by using one-component nonmagnetic toner T is used in the above developing apparatus 104, the toner ununiformly stays in a longitudinal direction of the developing sleeve 121 in the vicinity of an abutting nip portion of the developing blade 122 and the developing sleeve 121 so that an image defect (poor image) is caused. Further, when the developing operation is repeated many times, a staying toner amount becomes excessive so that the toner drops from the developing apparatus. Therefore, an image defect is caused and no developing apparatus can be used.
As shown in FIG. 18, the toner accumulating in a portion of the abutting portion of the developing sleeve 121 and the developing blade 122 on its downstream side in the rotating direction of the developing sleeve, i.e., in a wedge-shaped portion A. The accumulating toner is gradually grown in the wedge-shaped portion A by rotating the developing sleeve 121 at a time of the developing operation and finally becomes a cohering lump of the toner. This cohering lump drops from the wedge-shaped portion A as the developing sleeve 121 is rotated, thereby causing an image defect.
At this time, it has been found that cohering degrees of the toner staying in the wedge-shaped portion A and the toner within the developing container 126 are increased and the cohering lump is easily caused in the toner of a high cohering degree.
This phenomenon is notable when fine powder of a positive charging property and fine powder of a weak charging property charged in a polarity reverse to that of the toner are externally added as an external additive to the toner of a negative charging property to improve the transfer property and the developing property. Further, this phenomenon is also notable when a polishing agent component for preventing filming and melting attachment of the toner to the photosensitive drum, etc. is externally added to the toner.
When the above-mentioned magnetic toner is used, such a problem is not caused. The reasons for this are not clear, but it is considered that this is because the magnetic toner is borne to the developing sleeve in a brush shape, but the nonmagnetic toner is borne to the developing sleeve in a layer shape.
An object of the present invention is to provide a developing apparatus capable of stably forming a thin layer of nonmagnetic toner on a developer bearing member.
Another object of the present invention is to provide a developing apparatus in which the accumulation of toner in a longitudinal direction is prevented in the vicinity of an abutting portion of a developer bearing member and a developer regulating member and a thin layer of nonmagnetic toner can be stably formed on the developer bearing member, and an image of high quality can be obtained by performing a preferable developing operation.
Another object of the present invention is to provide a developing apparatus in which a thin layer of toner can be stably formed on a developer bearing member even when powder charged in a polarity reverse to that of the toner is externally added to this toner, and an image of high quality can be similarly obtained.
Another object of the present invention is to provide a developing apparatus comprising:
a developer bearing member for bearing and carrying a nonmagnetic developer;
a layer thickness regulating member for regulating a layer thickness of the developer borne by the developer bearing member;
developing bias applying means for applying an alternating current voltage to the developer bearing member; and
regulating member bias applying means for applying a direct current voltage to the layer thickness regulating member;
wherein when DC1 is an effective value of the alternating current voltage applied to the developer bearing member and DC2 is a value of the direct current voltage applied to the layer thickness regulating member, the direct current voltage value DC2 has a polarity, which is reverse to a charging polarity of the developer with respect to the effective value DC1.
Another object of the present invention is to provide a developing apparatus comprising:
a developer bearing member for bearing and carrying a nonmagnetic developer;
a layer thickness regulating member for regulating a layer thickness of the developer borne by the developer bearing member;
developing bias applying means for applying a direct current voltage to the developer bearing member; and
regulating member bias applying means for applying an alternating current voltage to the layer thickness regulating member;
wherein when DC1 is an effective value of the alternating current voltage applied to the developer bearing member and DC2 is a value of the direct current voltage applied to the layer thickness regulating member, the direct current voltage value DC2 has a polarity, which is reverse to a charging polarity of the developer with respect to the effective value DC1.
Another object of the present invention is to provide a developing apparatus detachably attachable to a main body of an image forming apparatus, comprising:
a developing apparatus side contact connected to an apparatus side contact of the main body of the image forming apparatus when the developing apparatus is mounted to the apparatus main body;
a developer bearing member for bearing and carrying a nonmagnetic developer, wherein a bias voltage can be applied to the developer bearing member by connecting the developing apparatus side contact to the apparatus side contact; and
a layer thickness regulating member for regulating a layer thickness of the developer borne by the developer bearing member, wherein the bias voltage can be applied to the layer thickness regulating member by connecting the developing apparatus side contact to the apparatus side contact.